I rarely delete a photo from an online host, so it's unlikely to be a problem for my images (and if there is an issue, let me know because it's a problem with my whole account.)

If people are linking from free accounts, they need to check that the links still deliver if they exceed maximum uploads. Some sites like Flickr will let you show the latest 200 posts, but will still host photos that are in excess of the 200 (it's a kind of underhanded prompt to get people to pay annually for the full account.)

Nope, leave them up, Flickr will still host websize versions, you just won't be able to scroll back and see them thru your Flickr acct. They will however continue to show up wherever you've linked them, like here.

As far as I know, photobucket (as annoying as their free service is) has no limits. They used to have total stoage limits, but I think they even did away with that. I guess they figure they will just kill you with dive bombing ads.